Proof Schemata for Theories equivalent to $PA$: on the Benefit of Conservative Reflection Principles

Abstract

Induction is typically formalized as a rule or axiom extension of the LK-calculus. While this extension of the sequent calculus is simple and elegant, proof transformation and analysis can be quite difficult. Theories with an induction rule, for example Peano arithmetic do not have a {\em Herbrand} theorem. In this work we extend an existing meta-theoretic formalism, so called proof schemata, a recursive formulation of induction particularly suited for proof analysis, to Peano arithmetic. This relationship provides a meaningful conservative reflection principle between \PA and an alternative proof formalism. Proof schemata have been shown to have a variant of Herbrand's theorem for classical logic which can be lifted to the subsystem of our new formalism equivalent to primitive recursive arithmetic.